1. M. A. Clarke-GaytherRAL/FETS/HIPPI Beam Chopper Development for Next Generation High Power Proton Drivers Michael A. Clarke-Gayther RAL / FETS / HIPPI

2. M. A. Clarke-GaytherRAL/FETS/HIPPI  Overview  Fast Pulse Generator (FPG)  Slow Pulse Generator (SPG)  Slow – wave electrode designs  Summary Outline

3. M. A. Clarke-GaytherRAL/FETS/HIPPI Overview

4. M. A. Clarke-GaytherRAL/FETS/HIPPI Overview HIPPI WP4: The RAL† Fast Beam Chopper Development Programme Progress Report for the period: July 2005 – December 2006 M. A. Clarke-Gayther † † STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK EU contract number RII3-CT-2003-506395CARE-Note-2007-002-HIPPI

5. M. A. Clarke-GaytherRAL/FETS/HIPPI Overview The RAL Front-End Test Stand (FETS) Project / Key parameters

6. M. A. Clarke-GaytherRAL/FETS/HIPPI Overview RAL ‘Fast-Slow’ two stage chopping scheme

7. M. A. Clarke-GaytherRAL/FETS/HIPPI Overview 3.0 MeV MEBT Chopper (RAL FETS Scheme C) Chopper 1 (fast transition) Chopper 2 (slower transition) ‘CCL’ type re-buncher cavities 3.2 m

8. M. A. Clarke-GaytherRAL/FETS/HIPPI Overview FETS Scheme A / Beam-line layout and GPT trajectory plots Losses: 0.1 % @ input to CH1, 0.3% on dump 1 0.1% on CH2, 0.3% on dump 2 Voltages: Chop 1:+/- 1.28 kV (20 mm gap) Chop 2:+/- 1.42 kV (18 mm gap)

9. M. A. Clarke-GaytherRAL/FETS/HIPPI Overview KEY PARAMETERSSCHEME ASCHEME BSCHEME C ION SPECIESH- ENERGY (MeV)3.0 RF FREQUENCY (MHz)324 BEAM CURRENT (mA)40 - 60 NORMALISED RMS INPUT EMITTANCE IN X / Y / Z PLANES ( π.mm.mr & π.deg.MeV) 0.25 / 0.25 / 0.18 RMS EMITTANCE GROWTH IN X / Y / Z PLANES (%)6 / 13 / 24 / 8 / 05 / 8 / 0 CHOPPING FACTOR (%)30 - 100 CHOPPING EFFICIENCY (%)99.9 FAST CHOPPER PULSE: TRANSITION TIME / DURATION / PRF/ BURST DURATION / BRF 2 ns / 12 ns / 2.6 MHz / 0.3 – 2 ms / 50 Hz 2 ns / 15 ns / 2.6 MHz / 0.3 - 2 ms / 50 Hz FAST CHOPPER ELECTRODE EFFECTIVE LENGTH / GAPS (mm)450 x 0.82 = 369 / 20 FAST CHOPPER POTENTIAL(kV)± 1.3± 1.2± 1.4 SLOW CHOPPER PULSE: TRANSITION TIME / DURATION / PRF/ BURST DURATION / BRF 12 ns / 100 ns – 0.1 ms 1.3 MHz / 0.3 – 2 ms / 50 Hz 12 ns / 100 ns – 0.1ms 1.3 MHz / 0.3 -2 ms / 50 Hz 15 ns / 100 ns – 0.1 ms/ 1.3 MHz / 0.3 - 2 ms / 50 Hz SLOW CHOPPER EFFECTIVE LENGTH / GAPS (mm)450 x 0.85 / 18 450 x 0.85 / 14 SLOW CHOPPER POTENTIAL (kV)± 1.5± 2.0± 5.0 POWER ON FAST / SLOW BEAM DUMPS (W)150 / 850 OPTICAL DESIGN CODE(S)GPT

10. M. A. Clarke-GaytherRAL/FETS/HIPPI Fast Pulse Generator (FPG) development

11. M. A. Clarke-GaytherRAL/FETS/HIPPI FPG development 9 x Pulse generator cards High peak power loads Control and interface Combiner 9 x Pulse generator cards Power supply 9 x Pulse generator cards 1.7 m SPG / Front View

12. M. A. Clarke-GaytherRAL/FETS/HIPPI FPG development SPG waveform measurement / HTS 81-06-GSM-CF-HFB

13. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow Pulse Generator (SPG) development

14. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development 16 close coupled ‘slow’ pulse generator modules Slow chopper electrodes Beam SPG beam line layout and load analysis

15. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development Two turn load inductance ~ 50 nH Load capacitance ~ 30 pf 6 kV, 400 MHz ÷ 1000 probe - 8 kV ~ 5 μF LF cap. bank + 8 kV ~ 5 μF LF cap. bank - 8 kV ~ 3 nF HF cap. bank + 8 kV ~ 3 nF HF cap. bank HV dampin g resistor 8 kV push-pull MOSFET switch Trigger input Auxiliary power supplies Cooling fan 8 kV SPG pre-prototype Test Set-up

16. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development SPG waveforms at ± 6 kV peak & 50 ns / div. SPG waveforms at ± 6 kV peak & 2.0 μs / div. SPG waveforms at ± 6 kV peak & 50 ns / div. SPG waveform measurement /HTS 81-06-GSM HFB SPG waveforms at ± 6 kV peak & 50 μs / div. T r =15.5 ns T f =19.7 ns T r =11.9 ns T f =11.1 ns

17. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development Pulse ParameterESS Requirement MeasuredCompliancyComment Amplitude (kV into 50 Ohms)± 6.0± 4.0Yes± 4 kV rated Transition time (ns)~ 12.0T rise ~ 13, T fall ~ 12LimitedFirst ~ 10 pulses Duration (μs)0.2 – 100 YesFWHM Droop (%)00YesDC coupled Repetition frequency (MHz)1.2 Yes Burst duration @ 1.2 MHz1.5 ms YesBurst limitation Burst repetition frequency (Hz)50 YesDuty cycle ~ 0.27 % Post pulse aberration (%)± 2≤ ± 2Yes Pulse width stability (ns)± 0.1≤ ± 0.1Limited+ve shifting, -ve OK Timing stability (ns over 1 hour)± 0.5± 0.4YesPeak to Peak Burst amplitude stability (%)+ 10, - 5< + 10, -5Yes@ 0.1 MHz PRF Measured performance parameters / HTS 81-06-GSM HFB 8kV SPG

18. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development Prototype 8 kV SPG euro-cassette module / Side view Low-inductance HV damping resistors 8 kV push-pull MOSFET switch module High voltage feed-through (output port) Axial cooling fans Air duct 0.26 m

19. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development SPG Development Plan / October 2006  Bench test 4 kV rated switch Compare results with existing 8 kV rated switch  Re-formulate specification for SPG Based on new optical design for FETS  Obtain quotes for a custom designed switch Based on re-formulated specification for FETS

20. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development BEHLKE HTS 41-06-GSM-CF-HSB (4kV) & 81-06-GSM-CF-HSB (8kV)

21. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development 4kV MOSFET switch (BEHLKE HTS 41-06-GSM-CF-HSB) / Test Set-Up

22. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development 4kV MOSFET switch (BEHLKE HTS 41-06-GSM-CF-HSB) / Test Set-Up

23. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development SPG waveforms at ± 4 kV peak & 50 ns / div. SPG waveforms at ± 4 kV peak & 2.0 μs / div. SPG waveforms at ± 4 kV peak & 50 ns / div. SPG waveform measurement / HTS 41-06-GSM-CF-HFB (4 kV) SPG waveforms at ± 4 kV peak & 50 μs / div. T r =11.2 ns T f =10.8 ns T r =12.0 ns T f =10.8 ns

24. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development Measured performance parameters / HTS 41-06-GSM-CF-HSB (4kV)

25. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development Measured performance parameters / HTS 41-06-GSM-CF-HSB (4kV)

26. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development Fast-Slow Chopper / FPG & SPG synchronisation / ESS Timing FPG (0.2 ms/div.) FPG (4.0 μs/div.) SPG (0.2 ms/div.) SPG (4.0 μs/div.)

27. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development FPG (0.2 ms/div.) FPG (4.0 μs/div.) SPG (0.2 ms/div.) SPG (4.0 μs/div.) Fast-Slow Chopper / FPG & SPG synchronisation / ESS Timing

28. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development Pulse ParameterFETS Requirement MeasuredCompliancyComment Amplitude (kV into 50 Ohms)± 1.5± 4.0Yes± 4 kV rated Transition time (ns)~ 12.0T rise ~ 12, T fall ~ 11Yes500 pulses Duration (μs)0.23 – 1000.17 – 100YesFWHM Droop (%)00YesDC coupled Repetition frequency (MHz)1.3 Yes Burst duration @ 1.2 MHz0.3 – 1.5 ms0.4 msLimitedScalable Burst repetition frequency (Hz)5020LimitedScalable Post pulse aberration (%)± 5≤ ± 5YesAdjustable Pulse width stability (ns)± 0.18.2 ns (n=1 to 2)Limited Can be corrected Timing stability (ns over 1 hour)± 0.5--Not yet measured Burst amplitude stability (%)+ 10, - 5< + 10, -5Yes0.4 ms burst Measured performance parameters / HTS 41-06-GSM-CF-HSB (4kV) SPG

29. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development Summary / 4 kV SPG development  Transition time and transition time stability are now compliant (just) with four bunch chopping at 324 MHz.  Maximum burst duration at 50 Hz BRF will be tested with an upgraded auxiliary power supply and improved cooling.  Timing stability (jitter) will be tested when the auxiliary power supply and cooling have been upgraded.  The 4kV SPG results are encouraging – particularly the improved transition time and pulse duration stability.

30. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development

31. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Where: Transverse extent of the beam: L2 Beam transit time for distance L1: T(L1) Pulse transit time in vacuum for distance L2: T(L2) Pulse transit time in dielectric for distance L3: T(L3) Electrode width: L4 For the generalised slow wave structure: Maximum value for L1 = V1 (T3 - T1) / 2 Minimum Value for L1 = L2 (V1/ V2) T(L1) = L1/V1 = T(L2) + T(L3) The relationships for field (E), and transverse displacement (x), where q is the electronic charge, is the beam velocity, m 0 is the rest mass, z is the effective electrode length,  is the required deflection angle, V is the deflecting potential, and d is the electrode gap, are: ‘E-field chopping / Slow-wave electrode design

32. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Strategy for the development of RAL slow–wave structures  Modify ESS 2.5 MeV helical and planar designs Reduce delay to enable 3 MeV operation Increase beam aperture to ~ 20 mm Maximise field coverage and homogeneity Simplify design - minimise number of parts Investigate effects of dimensional tolerances Ensure compatibility with NC machining practise Identify optimum materials  Modify helical design for CERN MEBT Shrink to fit in 95 mm ID vacuum vessel

33. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development ESS planar and Helical slow-wave electrode designs Planar AHelical BHelical C

34. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Planar structure A 3D cut-away 300 mm

35. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Helical structure B with L - C trimmers and adjustable delay

36. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Helical structure B1

37. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Helical structure B1Helical structure B2

38. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Helical structure B1Helical structure B2

39. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Helical structure B1Helical structure B2

40. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development 8.0 mm radius inscribed circle RAL helical B / Field in x - y plane/ line integrals along z

41. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development ‘On-axis field in x, y plane

42. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Simulation of Helical B structure in the T & F domain

43. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development RAL Planar A2 (3.0 MeV design)

44. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development RAL Planar A2 (3.0 MeV design)

45. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Selection of coaxial and strip-line dielectric support material AL 2 O 3 AlNShapal M MACORBN (HBR) VespelPEEK Dielectric constant (1 MHz) 9.4-9.98.76.95.94.13.553.3 Loss Tangent (1 MHz) < 1 e-3 5 e-41 e-35 e-3< 5 e-43 e-3 Thermal conductivity (W/m o C) 25 - 30170961.533 - 550.350.25 Flexural Strength MPa~ 400 ~ 250~ 100~ 50~ 100~ 150 Service temperature (In vacuum) 1500100015008001000350300 Metallise-ableYY* ?N?? Machine-ableDiamond YYYYY

46. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Vacuum coaxial support disc / HF Simulation

47. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Semi-rigid to vacuum coaxial transition / HF Simulation

48. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Coaxial to strip-line 90° transition / HF simulation

49. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Planar strip-line stand-off / HF simulation

50. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Planar strip-line components / HF simulation Beam aperture 180 degree bend

51. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Strip-line dimensional tolerance analysis Plot variation in Z 0 with: Strip width Displacement in x & y planes Strip edge radius Strip thickness

52. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Strip-line dimensional tolerance analysis

53. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Strip-line dimensional tolerance analysis

54. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Visualisation and development of 3D models

55. M. A. Clarke-GaytherRAL/FETS/HIPPI Slow-wave electrode development Design parameter Planar A1 & A2Helical B1Helical B2Helical C ESSFETSESSFETS ESSFETS H‾ beam energy (Mev)2.53.02.53.0 2.53.0 Beam velocity (m/s)2.18292e72.39032e72.18292e72.39032e7 2.18292e72.39032e7 Beam width / 100% (mm)1018101810 18 Beam aperture (mm)11191119 1119 Cell periodicity (mm)19 Cell delay (ns)0.8703940.7948740.8703940.794874 0.8703940.794874 Coverage factor: Centre / Edge (%) 80 / 7782 / 8180 / 7581 / 7982 / 8180 / 7782 / 81 Characteristic impedance (Ω)50 ± 0.5 External dimensions (mm) 45 x 300 x 400 45 x 280 x 450 < 75 rad. x 400 < 48 rad. x 450 < 70 rad. x 450 < 75 rad. x 400 < 70 rad. x 450 RAL slow-wave electrode structures / Key parameters

56. M. A. Clarke-GaytherRAL/FETS/HIPPI Summary  FPG Meets most key specifications  SPG 4 kV version looks promising  Slow-wave electrode designs Planar and Helical designs now scaled to 3.0 MeV Beam aperture increased to 19.0 mm HF models of components with trim function Analysis of coverage factor Analysis of effect of dimensional tolerances Identification of optimum materials / metallisation Identification of coaxial components and semi-rigid cable Designs compatible with NC machining practice As usual – the Devil is in the details!